由於使用者增多以及網路傳輸速率越來越快的環境下，需要提供更多的能源來讓網路能夠運作。乙太被動光纖網路是所有接取網路中較為省電的架構之一。光纖網路單元(ONU)並不會在所有的時間接收與傳送資料，有三種浪費能源的主要原因，竊聽(overhearing)、控制封包開支(control packet overhead)與閒置聆聽(idle listening)，若能讓ONU進入睡眠模式，則可以節省能源。目前ONU的transmitter與receiver的實作可以分成兩類，第一種為ONU的傳輸端與接收端同時關閉，傳送端與接收端有可能會互相影響無法讓沒有資料需要運作的一端進入睡眠模式，第二種為傳送端與接收端分開關閉，此方式可以解決第一種的問題。
當ONU的傳送端在睡眠模式中，光纖連結終端(optical line terminal)可以根據上傳的開始時間告知ONU的傳送端醒來時間，當ONU的接收端在睡眠模式中，ONU無法接收任何資料，因此OLT必須要先計算醒ONU的接收端睡眠時間，讓ONU可以順利接收資料。
本論文透過OLT下傳的開始時間來計算ONU的接收端睡眠時間，提出的方法使用兩種不同的方式預測OLT的開始下傳時間。OLT同時使用這兩種方式計算ONU接收端的睡眠時間，採取睡眠時間最長的為ONU接收端的睡眠時間。從模擬結果確實可以看出本論文的方法可以有效地增加ONU的接收端睡眠時間，達到有效的能源節省且不會使ONU接收端的睡眠時間越來越長的情況發生，造成下傳封包延遲的時間增加。

The number of users and the data rate are increasing in recent years. The access network needs more energy to satisfy the demands. The EPON is one of the most energy saving architecture in the access network. The ONU does not transmit or receive data all the time. There are three major sources for energy wasting including overhearing, control packet overhead, and idle listening. Therefore, the ONU can enter into sleep mode can save more energy.
There exist two implementation options for ONU’s transmitter and receiver. In option 1, the ONU’s transmitter and receiver are turned off simultaneously. The transmitter and receiver could be affected by each other. The transmitter or receiver could not be turned off separately when there is no data to transmit or receive. In option 2, the ONU’s transmitter or receiver is turned off or on separately to eliminate the option 1 problem.
When the ONU’s transmitter enters into sleep mode, it is easy for OLT to wake up the ONU’s transmitter through the upstream start time in the received GATE message. When the ONU’s receiver enters into sleep mode, the ONU can’t receive any data. Therefore, the OLT should assign sleep time for the ONU’s receiver before the ONU enters into sleep mode.
The thesis uses OLT’s downstream start time to calculate the sleep time of ONU’s receiver. The proposed method uses two different cases to predict downstream start time by the OLT. First, the OLT uses upstream scheduling result to predict the downstream start time. The OLT uses the two cases method simultaneously, and the result of longer is the sleep time of ONU’s receiver. In the simulation result, the sleep time of ONU’s receiver is increased and more power is saved. The downstream packet delay doesn’t increase because the sleep time isn’t too long.

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